By and large no matter how well a hay field is managed there will come a time when it will need to be renovated, started over.
When “June grass” junk grasses start moving in it is only a matter of time before they start to become the “dominate” grass. They are an annual and put out a prolific amount of seeds. Each year getting exponential. I am told they can be somewhat controlled by using a pre-emergent. But this is not cheap.
The same can be said for weeds, thistle and such. But these are easier to get rid of, control than junk grasses.
Both Timothy and Orchard are clump grasses. The plant grows and continues to grow from a “clump” of roots. It does not spread like lawn grass continuously forming, making new grass/plants and covering all of the soil surface leaving little room, open soil for weeds etc to move in.
Me, I would cut close and bale all of the junk that is on it. Cattle people might be interested in taking it off you hands.
Take soil samples from different locations around the field and mark the locations on the bags. So you don’t wast money on over fertilizing ares that may not need as much.
I would then have it plowed under deep as possible. So any junk seeds left will be buried too deep to grow. Have it floated/leveled well and rolled tight. Unless you are going to broadcast seed it. I think it would be best to drag after being floated then broad cast seed, drag again and then rolled tight.
If the seed it going to be drilled then it should be rolled tight before drilling. Either way maybe area/soil specific. Your local hay producers would know the best way to go about and the timing. IMO and experience they are FAR more knowledgeable than extension agents. Very few of which have ever personally planted hay let alone grown, baled and sold it.
Around here smooth Bromegrass hay seed is is mixed with the Timothy and or Orchard seeds when planted. It is a sod-forming perennial grass with deep roots. The grass is highly palatable and is high in protein content and relatively low in crude-fiber content. The Bromegrass fills in the areas around the clumps of Tim or Orchard. Leaving less opportunity for weeds and junk grasses to move in. So you will also get a better yield.
Wish I had been advised to do this when I planted pure stand of Orchard/Tim 12+ years ago. I am battling junk grasses and it only a matter of time until I loose the battle.